1.

If 7 times the 7th term of an A.P is equal to the 11 times its 11th term, show that its 18th termis zero.OR

Answer»

7×t7 = 11×t11 tn=a+(n-1)dt7=a+6d t11=a+10d 7(a+6d)= 11(a+10d) 7a+42d=11a+110d 4a+68d=0 a+17d=0 a=-17d t18=a+17d =-17d+17d =0



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